1. Field of the Invention
The present invention relates to a controller for controlling a power converter to output constant power and a related method thereof, and particularly to a controller and a related method thereof that can control a power converter to output constant power through a secondary side of the power converter.
2. Description of the Prior Art
In the prior art, when a secondary side of a power converter is overload, an output current of the secondary side of the power converter can be increased to respond to overload of the secondary side of the power converter. Meanwhile, because the output current of the secondary side of the power converter is increased, a feedback current generated by a feedback circuit (e.g. a photo coupler) of the secondary side of the power converter is decreased, resulting in a power switch controller of a primary side of the power convertor increasing a duty cycle of a power switch of the primary side of the power convertor. Meanwhile, although the power switch controller of the primary side of the power convertor has entered a deep continuous current mode (CCM), because the duty cycle of the power switch of the primary side of the power convertor can not be increased infinitely in an over-current protection mode, the secondary side of the power converter cannot maintain a fixed output voltage, resulting in output power of the secondary side of the power converter being gradually decreased. In addition, the prior art can simultaneously control the output current and the output voltage of the secondary side of the power converter through a primary-side regulation constant current/constant voltage technology. However, in the primary-side regulation constant current/constant voltage technology, if the output current of the secondary side of the power converter exceeds a fixed current value, the output current of the secondary side of the power converter is still limited to the fixed current value, resulting in the output power of the secondary side of the power converter being still not maintained at a constant value. Therefore, when the secondary side of the power converter is overload, the output power of the secondary side of the power converter can not be maintained at a constant value, so a next stage circuit coupled to the secondary side of the power converter may not operate normally.